For a while, floppy disks were good enough for storing data. As time went by, more data was used by people. For computer users, this meant two things. Firstly, many more disks had to be used for one set of data. This made it a nuisance to save and load data, especially if the data was going to be used on the same computer at all times.

Secondly, more time was wasted. It took a lot of time to load all of the data, especially if it was spanning many diskettes. Everything would have to be loaded every time the computer was turned on. Floppy disk speeds could not advance greatly, simply because the floppy disk was an external diskette that was not in the computer permanently.

The answer was an internal device inside the computer, called the Hard Drive. The Hard Drive provides the same function as the Floppy Disk, with two distinct differences. It is much faster, and holds much more data. This provided an excellent solution to the storage problem. The Hard Drive could also advance at a much quicker pace than the Floppy Disk Drive.

Picture of a Maxtor Hard Drive
© 2001 by www.maxtor.com

The actual data which gets stored on the hard drive is stored on Platters. Here is an illustration of several platters and how they are divided:

Name	Description
Platter	A flat, circular disc, having a similar shape to a CD. It holds the physical data. Platters can usually store data on the top and bottom side at the same time. Most modern CD-ROM Drives have multiple platters in order to allow for more storage capacity.
Track	A concentric set of magnetic bits on a platter. The track is divided into many sectors.
Cylinder	A group of tracks with the same radius. On the above, one of the parts labeled red would be a track by itself, but all of the red parts would together be addressed as a cylinder.
Sector	A small part of a track. Every sector has its own unique ID number, as well as an error correction code. The error correction code ensures that if there is a data error on the sector, it can be repaired, and the data can be used.

Although the platter is only a few millimetres thick, there are usually six layers to a platter. Before we get to the diagram, we need to know that 1 mm (millimetre) = 100,000 nm (nanometres). Keeping this in mind, here is the cross section of a small part of the platter (not to scale):

Color	Thickness	Layer Content
	1 nm	Lubricant - used to minimize the wear of the carbon layer
	30 nm	Magnetic Layer - Stores the bits of data
	15 nm	Carbon Overcoat - increases the corrosion of the Magnetic layer
	50 nm	Chromium - used as an under-layer for the magnetic layer
	10,000 nm	Nickel Phosphide Layer - separates the metal and the magnetic layer
	0.5 mm or more	Metal - used to give the platter strength

The illustration below shows an image of the Hard Drive's Read Head, Write Head, and a Platter.

Before we start with the Read and Write head, we need to establish the difference between how 0s and 1s are stored on the Hard Drive. Each bit of data on the hard drive is stored on one small particle of magnetic metal. Each of these pieces of metal has its own poles, the north pole and the south pole. When there is no data on the hard drive, the north and south poles of all of the magnetic particles are facing in the same direction. In other words, all the arrows in the diagram above would face the same way as the large arrow below the platter in the diagram. The Write head (B) acts as an electromagnet. If it wants the particle below it to store a 1, the wire wrapped around it sends current through it one way, causing the poles to shift one way. In contrast, if it wants to store a 0, the wire wrapped around it sends the current the opposite way, causing the poles to shift again. An opposite direction of the current causes the poles to switch, and the arrow to face the other way.

The Read Head (A) has a Magneto-Resistive sensor, along with two shields which shield out any potential interference.

Today's Hard Drive performance is more than 50 times faster then when it debuted in the 80s. When they first came out, the Hard Drive could only spin at a mere 500 RPM (Rotations Per Minute). Today 7,200 RPM Hard Drives are a standard, which is faster than the RPM of most family cars. There are also high performance hard drives that go up to 15,000 RPM, which is faster than most, if not all of the sports cars in the world. Moreover, techniques have been developed to get more data from every rotation, allowing for even faster speeds.

As for Hard Drive storage capacity, this is also increasing. It is not rare anymore to see hard drives as big as 20-30 Gigabytes. Hard Drives over 100 GB are available on the market, while a few Terabyte Hard Drives do exist.